1. Technical Field
The present invention relates to a vehicle occupant safety apparatus and, in particular, to a vehicle seat belt system including a seat belt webbing height adjuster and a pretensioner for taking up slack in the seat belt in the event of a vehicle collision.
2. Description of the Prior Art
Vehicle seat belt systems use seat belt webbing to restrain movement of a vehicle occupant. It is known to include a pretensioner in such a system. In the event of vehicle deceleration above a predetermined threshold level, such as occurs in a vehicle collision, the pretensioner is actuated to tension the belt webbing and to take up slack in the belt webbing.
It is also known to include a manually adjustable seat belt webbing height adjuster in a seat belt system. The belt webbing passes through a seat belt webbing guide or D-ring that is supported on the height adjuster at a location adjacent to the shoulder of the vehicle occupant. The height adjuster enables the vehicle occupant to set the vertical position of the D-ring to one of several vertically spaced locking positions. In some height adjusters, the D-ring can, at times, be positioned vertically between locking positions.
Some seat belt systems include both a pretensioner and a height adjuster. When the pretensioner is actuated, the tensioned belt webbing exerts a strong downward force on the D-ring. If the pretensioner is actuated when the D-ring is not at a locking position, the D-ring is pulled downward along the height adjuster until it locks. It is desirable to ensure that the D-ring locks at the next available downward locking position and does not skip past one or more locking positions before engaging.